Ok, given that this is working, do you have any suggestions/ideas on how to handle the pair-production issue from a analysis point of view or know people who have dealt with similar problems?

If I consider those cases in which the particle of interest was reconstructed but at least one photon did pair production as background, I lose a huge fraction of my signal.
If I consider those cases as signal, I certainly have a systematic error I have to correct for (maybe some sort of energy-correction based on the multiplicity in an event?)